Golf balls are made in a variety of constructions and compositions. In this regard, each of the golf ball core, intermediate layer, and cover may be single layered or comprise multiple layers. Examples of golf ball materials range from balata to polybutadiene, ionomer resins, polyurethanes, and/or polyureas. Typically, outer layers are formed about the spherical outer surface of an inner golf ball component via compression molding, casting, or injection molding.
Golf ball manufacturers continuously experiment with golf ball constructions and material formulations in order to target and improve aerodynamic and/or inertial properties and achieve desired feel without sacrificing durability. In this regard, sufficient adhesion between golf ball layers is essential in achieving adequate impact durability. Without a satisfactory amount of adhesion between these layers, both the impact durability as well as the shear resistance of the cover can suffer.
This issue typically presents when the materials of adjacent golf ball layers don't bond together well. For example, the bond strength or “adhesive strength” between an ionomeric casing/intermediate layer and a polyurethane cover layer may be unacceptably low.
Poor interlayer bond or adhesive strength can result in layer separation or “delamination” when the golf ball is struck by a club. Layer separation may be visually apparent as “bubbling” or air pockets between the two layers. Delamination detrimentally affects not only the appearance of the golf ball but playability as well. Accordingly, golf ball manufacturers look for cost effective compounds and methods for addressing this problem in order to preserve brand recognition and reputation.
Currently, several different types of adhesion promoting pre-treatment processes exist for addressing cut and shear issues caused by lack of adhesion between layers. Examples of pretreatments include surface roughening; surface energy modifications such as corona, plasma, and flame treatments; adhesives; adhesion promoters and combinations thereof. Adhesives are typically applied via spray or dip and usually require a drying and post cure step. Adhesion promoters are likewise usually applied by dip or spray, followed by rinsing and drying steps.
In this regard, silane adhesion promoter surface pretreatments and tie layers have been used to improve interlayer adhesion between adjacent differing mated layers. See, e.g., commonly owned U.S. Pat. No. 6,926,621 of Lutz. et al., hereby incorporated herein in its entirety. With such surface pretreatments, the silane adhesion promoter, either neat (without solvent) or in solution, is exposed to or applied about the outer surface of one layer before mating or otherwise joining it with a second layer. The silane adhesion promoter provides a reactive surface for creating strong bonds between the treated layer and an adjacent different layer. However, silane-containing adhesion promoters have undesirably limited shelf lives once performed/applied and will fail to provide adequate adhesion between those layers unless molding follows within a short specified time window of the surface pretreatment or application of the tie layer.
Accordingly, silanes were eventually tried within the golf ball composition itself to improve one of intra-layer adhesion or inter-layer adhesion. See e.g., Kennedy et al. 2012/0083364. Later, in co-owned and related U.S. patent application Ser. No. 15/626,343, filed on Jun. 19, 2017 (“the '343 appl.”) and U.S. Pat. No. 9,713,748 (“the '748 patent”) of Binette et al., it was discovered that both inter-layer and intra-layer adhesion could be improved when a given amount of silane-containing adhesion promoter(s), within the range of from about 0.1 wt. % to about 5.0 wt. %, has a first required number of free functional groups to bond the second layer and the first layer at an interface in addition to a second required number of free functional groups bonding and/or crosslinking ingredients within the second layer.
Unfortunately, these same results aren't achieved when the layer incorporating silane-containing adhesion promoter(s) is white pigmented with TiO2. Accordingly, there remains a need to develop white-pigmented golf balls that can produce the same excellent dual inter-layer/intra-layer adhesion of non-pigmented layer formulations containing silane-containing adhesion promoter(s). Such golf balls, if meanwhile producible cost-effectively within existing golf ball manufacturing processes, would be particularly desirable and useful. The present inventive golf ball and method of making same addresses and solves these needs.